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List:       cfe-commits
Subject:    Re: [PATCH] D11490: [Concepts] Add diagnostic: non template declaration
From:       Aaron Ballman <aaron () aaronballman ! com>
Date:       2015-07-24 19:37:51
Message-ID: CAAt6xTsSZcvg6iQRHnAuxRFQoWwyc2XWDU9_isrc75KTFKJGow () mail ! gmail ! com
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On Fri, Jul 24, 2015 at 3:27 PM, Nathan Wilson <nwilson20@gmail.com> wrote:
>
>
> On Fri, Jul 24, 2015 at 2:14 PM, Aaron Ballman <aaron@aaronballman.com>
> wrote:
>>
>> On Fri, Jul 24, 2015 at 2:43 PM, Nathan Wilson <nwilson20@gmail.com>
>> wrote:
>> > nwilson created this revision.
>> > nwilson added reviewers: rsmith, faisalv, fraggamuffin,
>> > hubert.reinterpretcast.
>> > nwilson added a subscriber: cfe-commits.
>> >
>> > Adding diagnostic for concepts declared as non template (function or
>> > variable)
>> >
>> > http://reviews.llvm.org/D11490
>>
>> >
>> > Files:
>> >   include/clang/Basic/DiagnosticSemaKinds.td
>> >   lib/Sema/SemaDecl.cpp
>> >   test/SemaCXX/cxx-concept-declaration.cpp
>> >
>> > Index: test/SemaCXX/cxx-concept-declaration.cpp
>> > ===================================================================
>> > --- test/SemaCXX/cxx-concept-declaration.cpp
>> > +++ test/SemaCXX/cxx-concept-declaration.cpp
>> > @@ -15,3 +15,7 @@
>> >  struct C {
>> >    template<typename T> static concept bool D3 = true; // expected-error
>> > {{concept declarations may only appear in namespace scope}}
>> >  };
>> > +
>> > +concept bool D4() { return true; } // expected-error {{concept can only
>> > be applied to a function or variable template definition}}
>> > +
>> > +concept bool D5 = true; // expected-error {{concept can only be applied
>> > to a function or variable template definition}}
>> > Index: lib/Sema/SemaDecl.cpp
>> > ===================================================================
>> > --- lib/Sema/SemaDecl.cpp
>> > +++ lib/Sema/SemaDecl.cpp
>> > @@ -4865,6 +4865,12 @@
>> >      // C++ Concepts TS [dcl.spec.concept]p1: The concept specifier
>> > shall be
>> >      // applied only to the definition of a function template or
>> > variable
>> >      // template, declared in namespace scope
>> > +    if (!TemplateParamLists.size()) {
>> > +      Diag(D.getDeclSpec().getConceptSpecLoc(),
>> > +           diag::err_concept_decl_non_template);
>> > +      return nullptr;
>> > +    }
>> > +
>> >      if (!DC->getRedeclContext()->isFileContext()) {
>> >        Diag(D.getIdentifierLoc(),
>> >             diag::err_concept_decls_may_only_appear_in_namespace_scope);
>> > Index: include/clang/Basic/DiagnosticSemaKinds.td
>> > ===================================================================
>> > --- include/clang/Basic/DiagnosticSemaKinds.td
>> > +++ include/clang/Basic/DiagnosticSemaKinds.td
>> > @@ -1966,6 +1966,8 @@
>> >    "use __attribute__((visibility(\"hidden\"))) attribute instead">;
>> >
>> >  // C++ Concepts TS
>> > +def err_concept_decl_non_template : Error<
>> > +  "concept can only be applied to a function or variable template
>> > definition">;
>>
>> Since we are using "concept" as a grammar term, I think we want to
>> quote it. Similar diagnostics suggest phrasing like:
>>
>> "'concept' can only appear on a function template or variable template
>> definition"
>>
>> This also reduces some ambiguity over how "function or variable template"
>> binds.
>>
>> ~Aaron
>
>
> May we apply both this suggestion and Hubert's? So it would be:
>
> "the 'concept' specifier may only be applied to the definition of a function
> or variable template"

I don't have a strong preference, but I think "specifier may only be"
is kind of wordy without adding much value. For comparison:

def err_inline_non_function : Error<
  "'inline' can only appear on functions">;
def err_noreturn_non_function : Error<
  "'_Noreturn' can only appear on functions">;
def err_virtual_non_function : Error<
  "'virtual' can only appear on non-static member functions">;
def err_explicit_non_function : Error<
  "'explicit' can only appear on non-static member functions">;

~Aaron

>
>>
>>
>> >  def err_concept_decls_may_only_appear_in_namespace_scope : Error<
>> >    "concept declarations may only appear in namespace scope">;
>> >  def err_function_concept_not_defined : Error<
>> >
>> >
>> >
>> > _______________________________________________
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>> > cfe-commits@cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>> >
>
>
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